"CBT improves depression by teaching individuals a host of adaptive coping skills that improve mood," said lead study author Roseanne Dobkin, a professor of psychiatry at Rutgers University Robert Wood Johnson Medical School in Piscataway, New Jersey.

"These include strategies for increasing involvement in meaningful, pleasurable, and social activities, problem-solving around physical limitations, relaxation training, and learning how to 'talk back' to extreme negative thoughts and to put them in more balanced perspective," Dobkin said by email.

For the study, 72 patients (age 65.22 +/- 9.63 ) and their caregivers were recruited from August 2015 through September 2017. Patients had Parkinson's disease for an average of six years and depression for nearly three years. Most were taking antidepressants, and many were already receiving other kinds of talk therapy.

Patient-caregiver dyads were randomized into an intervention group that received weekly, one-hour sessions of cognitive-behavioral therapy by telephone over three months, while also continuing their usual medical and mental health care, or into a control group that received usual care along with clinical monitoring by study staff and a resource list including major PD foundations and national and local mental health resources.

The cognitive-behavioral sessions in the intervention group focused on teaching new coping skills and thinking strategies tailored to each participant's experience with Parkinson's disease. Their care partners, such as a spouse, another family member, or a close friend, were trained to help the patient use these new skills between sessions. After the three months, participants could choose to continue the sessions up to once a month for six months.

At the beginning of the study, the participants had an average Hamilton Depression Rating Scale score of 21. Scores of 17 to 23 indicate moderate depression.

After three months of cognitive-behavioral therapy, Ham-D scores for the intervention group fell to an average of 14, which indicates mild depression. The control group had no meaningful change in scores.

In the intervention group, 40% met the criteria for being "much improved" in their depression symptoms, compared with no participants in the control group. At the six-month follow-up, participants in the intervention group had maintained their improvements in mood.

"Depression affects up to 50% of people with Parkinson's disease and may occur intermittently throughout the course of illness," Dobkin said.

"Additionally, in many instances, depression is a more significant predictor of quality life than motor disability," Dobkin added. "So easily accessible and effective depression treatments have the potential to greatly improve people's lives."

The study did not include people with very advanced Parkinson's disease or with dementia, so the results may not apply to them. Also, while insurance coverage for telemedicine is growing, it is not yet available in all cases or all states.

Even so, the results suggest that adding phone-based CBT to usual treatment may help improve mood for many patients with depression, said Dr. Gregory Pontone, director of Parkinson's Neuropsychiatry Clinical Programs at Johns Hopkins University School of Medicine, in Baltimore.

"Depression causes bad emotions, probably through a chemical process in the brain, these bad emotions become associated with negative thoughts, and negative thoughts lead to illness sustaining behaviors," Pontone, co-author of an editorial accompanying the study, said by email.

"CBT identifies these negative, sometimes 'automatic,' thoughts and rescripts them into more positive thoughts and associated behaviors," Pontone.

The benefits of the telephone aspect are in extending CBT to patients who otherwise would not have access and to shy individuals who might be more inclined to participate in this modality, Pontone said.

"For shy or 'avoidant' individuals a potential minor harm might be in reinforcing behaviors associated with isolation, i.e. if they otherwise were capable and had access to in-person services and activities," Pontone said. "Avoidance, rather than directly confronting fears or problems, is sometimes considered maladaptive coping."